Effect of soda-lime glass powder on alkali-activated binders: Rheology, strength and microstructure characterization

Abstract

Alkali-activated binders (AABs) have the potential to consume various types of cementitious waste materials, including coal ashes, municipal solid waste incinerator ash, palm-oil fuel ash, steel slags, mine tailings, cement kiln dust, ceramic tile residue, rice husk ash, and waste glass. This paper presents a study of alkali-activated cement paste produced with the substitution of the cementitious waste material soda-lime glass, which makes up the major proportion of the general glass waste stream. In the alkali-activated cement paste, crushed soda-lime glass powder (CG) was used as a replacement for class F fly ash (FA) from 0 to 30% by total solid weight, keeping the ground granulated blast furnace slag (GGBFS) content constant at 50%. The influence of activator molarity (4–8 M), alkaline liquid/solid binder (L/S) ratio (0.4–0.5) and different curing conditions (ambient air curing, wet curing, and short-term heat curing) on the rheology, strength, and microstructure of CG-substituted AABs was investigated and optimum conditions are suggested. According to the experimental results, both the workability and strength (compressive and tensile) of the AAB gradually increased with increasing level of substitution of FA by CG. Significant improvement in flow and setting time was seen with the addition of CG, even in mixtures with a low L/S ratio of 0.4. Both ambient and wet curing had more influence on the strength gain of AABs, especially after 28 days. Short-term heat curing resulted in high early strength gain. The dissolution of CG increased with increasing molarity (from 4 to 8 M) of the alkaline solution, which improved both strength and microstructure with curing time. Morphological and elemental analysis indicated an improvement of the microstructure of AABs due to the increased formation of calcium-dominant hydration products and hence reduced porosity with the substitution of CG. However, undissolved large-sized CG particles agglomerated in the binder without participating in the alkaline reactions. These agglomerated particles may induce micro-cracks due to weak bonding between the cement matrix and the smooth CG interface, which reduces the durability of AABs. Therefore, the inclusion of waste soda-lime glass powder with a mean diameter of 10–15 µm as a precursor in FA/GGBFS-based AAB as a replacement for FA is feasible and provides a good solution for waste material recycling.